Matt 16: "In reply he said to them: “When evening falls, you say, ‘It will be fair weather, for the sky is fire-red,’ and in the morning, ‘It will be wintry, rainy weather today, for the sky is fire-red but gloomy.’
Here this author has taken his source "Mark' and followed the immediate setting closely, the response is to a test from Pharisees.
Luke 12: 54 And he said also to the people, When ye see a cloud rise out of the west, straightway ye say, There cometh a shower; and so it is.
55 And when ye see the south wind blow, ye say, There will be heat; and it cometh to pass.
56 Ye hypocrites, ye can discern the face of the sky and of the earth; but how is it that ye do not discern this time?
57 Yea, and why even of yourselves judge ye not what is right?
Here this author has removed the setting and relocated the conversation as one of a series. Specifically, he is said to be addressing the 'crowd'. Interestingly the author also offers a different weather pattern. It has been suggested this might be because that red/morning meaning rain does not apply to all regions and the author made his own weather prediction. Also interesting is that the manuscripts of Matt are split on this. Many translations reflect this with brackets. The variant form follows Mark in having no weather commentary at all.
he answered by saying to them, '•An evil and adulterous generation seeks for a sign"